WELCOME TO SCIENCE FRIDAYS!

1. WELCOME TO SCIENCE FRIDAYS!

2. REFLEXES Presented by Ruth Williams

3. Overview • Introduce Reflexes • Anatomical Background • Visceral Reflexes • Somatic Reflexes • Importance of Testing Reflexes: Testing your Reflexes • View Cadaveric Tissues involved in Reflexes

4. What is a reflex? • A reflex is an automatic, involuntary response. • A reflex can be a response to a stimulus or to internal feedback. • Reflexes are necessary to survival.

5. What is the function of a reflex? • The function of a reflex is to maintain homeostasis. • Removes body from painful stimuli that could cause tissue damage. • Prevents body from suddenly falling and moving. • Maintains blood pressure, breathing rate, water intake, blood carbon dioxide levels (yawning), etc. • Protects us from irritants: coughing, sneezing, vomiting, etc.

6. Anatomical Background • A crash course in the nervous system: • What is a neuron? What is a nerve? • Spinal cord anatomy and physiology.

7. What is a neuron? • A neuron is the functional unit of the nervous system. • Neurons and their components can be found in the brain and spinal cord (two components of central nervous system, CNS) and peripheral tissues. • Functions: • Relay sensory and motor information from one tissue to another using electrochemical signals. • Act as integrating centers.

8. What is a neuron? • A neuron is composed of three main structures. • Cell body (soma, perikaryon) • Contains the components of a typical cell that conduct the normal processes of a living cell. • Responds to messages from dendrites by processing information. • Dendrites • Extensions of the cell body that are receptive to stimuli. • Conducts messages towards cell body. • Axons • A single extension of the cell body that transmits information from cell bodies to ‘other cells’. • ‘Other cells’ respond to messages by continuing the conduction of the message or physically doing work (e.g. muscle contraction).

9. What is a neuron? Web Anatomy, University of Minnesota

10. What is a neuron? • Types of neurons • Neurons can be categorized by the type of information/messages they are transmitting. • Sensory neurons • Motor neurons • Interneurons CNS Sensory neurons Motor neurons

11. What is a nerve? • A nerve is composed of the axons and dendrites of multiple neurons. • The cell bodies of these nerves are usually located in the CNS or right next to the CNS. • The nerve itself is located outside of the CNS. • Examples • Ulnar nerve • Sciatic nerve

12. What is a nerve?

13. What is a nerve? • Most nerves conduct messages to and from the CNS. • Messages conducted towards the CNS are sensory in nature – pain, touch, temperature. • Messages conducted away from the CNS are motor in nature – result in muscle contraction or gland secretion.

14. Spinal Cord Anatomy • The spinal cord houses a number of the cell bodies of the nerves located in the peripheral tissues. • As a result, the spinal cord acts as one of the integrating centers for reflexes.

15. Spinal Cord Anatomy • The spinal cord is housed within the vertebrate of the vertebral column. • The spinal cord extends from the base of the skull to vertebrate L2 (lumbar 2). • The spinal cord is composed of cervical, thoracic, lumbar and sacral regions (named for association with specific vertebrate).

16. Spinal Cord Anatomy • Again, because the spinal cord houses many of the cell bodies for the major nerves of the body, these nerves must be able to attach to the spinal cord. • Nerves attach to the spinal cord at two roots • Anterior root • Dorsal root • As you move away from spinal cord the two roots of each nerve merge to form the actual nerve.

17. Spinal Cord Anatomy The JayDoc Histo Web, University of Kansas

18. Spinal Cord Anatomy Brain Galaxy Art Gallery, Jaica A. Kinsman

19. Reflexes • Crash course almost over….. • A reflex is a response to a stimulus. • The actual anatomical and physiological basis behind a reflex is a reflex arc. • A reflex arc is the simplest of all nerve pathways. • A nerve pathway is the route messages or information travels through the nervous system. • Involves at least 2 neurons – a sensory and motor neuron.

20. Components of a Reflex Arc • There are 5 basic components to a reflex arc: • Sensory receptor – a nerve or specialized tissue located at the end of a sensory neuron that is the first structure to respond to a stimulus. • Sensory neuron – may act as the sensory receptor. • Spinal cord or brain tissue • Motor neuron • Effector organ/tissue – the tissue that responds to the message from the motor neuron. • Muscle • Gland

21. Types of Reflexes • There are two main groups of reflexes: • Somatic reflexes • Autonomic/visceral reflexes • How reflexes are categorized depends on the effector tissue involved.

22. Autonomic Reflexes • The effector tissues of autonomic reflexes are smooth muscle, cardiac muscle and glandular tissue. • Both the brain and spinal cord can act as integrating centers for autonomic reflexes. • Autonomic reflexes result in gastric juice secretion, mouth watering upon seeing/smelling/thinking about food, regulating blood pressure, adjusting heart rate to level of exercise, etc.

23. Somatic Reflexes • The effector tissue of somatic reflexes is skeletal muscle. • You have conscious control over all of your skeletal muscles. • Some skeletal muscle movements do not require your conscious thought. These movements occur without you consciously having to initiate the muscular movement. • Breathing, swallowing, blinking, ability to pull away from a hot object before you even sense the heat, etc.

24. Examples of Somatic Reflexes • There are three common somatic reflexes discussed in most anatomy and physiology courses. • Stretch (knee-jerk, patellar) reflex. • Withdrawal (flexor) reflex. • Crossed-extensor reflex.

25. Anatomy of a Stretch Reflex • Simplest reflex arc. • Involves two neurons. • 1. Doctor taps your patellar tendon with a Taylor Reflex Hammer. • 2. Tapping of the tendon causes muscle to stretch. • 3. Stretching of muscle stimulates specialized sensory receptors located in thigh muscles called muscle spindles to be stretched. • 4. Sensory dendrites in muscle spindles become stimulated. • 5. Sensory dendrites conduct message of stimulation towards spinal cord through a nerve.

26. Anatomy of a Stretch Reflex • 6. Sensory dendrite meets up with its cell body in the dorsal root. • 7. From the cell body, the axon conducts the information into the spinal cord. • 8. In the spinal cord, the sensory axon synapses with a motor neuron. • 9. The motor axon carries the message out of the spinal cord through the anterior root. • 10. The motor axon will synapse with the muscles of the thigh which results in contraction of the quadriceps muscle – response: knee extension.

27. Anatomy of a Stretch Reflex

28. Anatomy of a Withdrawal Reflex • Involves three neurons. • Function: remove a limb or body part form a painful stimulus. • 1. Step on a stone with your left foot. • 2. A sensory neuron acts as a sensory receptor and is stimulated by the stone. • 3. Sensory dendrites conduct message of stimulation towards spinal cord through a nerve. • 4. Sensory dendrite meets up with its cell body in the dorsal root.

29. Anatomy of a Withdrawal Reflex • 5. From the cell body, the axon conducts the information into the spinal cord. • 6. In the spinal cord, the sensory axon synapses with an interneuron. • 7. The interneuron synapses with a motor neuron in the spinal cord. • 8. The motor axon carries the message out of the spinal cord through the anterior root. • 11. The motor axon will synapse with the muscles of the thigh which results in contraction of the hamstring muscles – response: knee flexion.

30. Anatomy of a Withdrawal Reflex

31. Anatomy of a Crossed-Extensor Reflex • Associated with a withdrawal reflex of the lower limbs. • Prevents falls by shifting weight of body to unaffected limb. • 1. This reflex begins in the spinal cord. • 2. The same sensory neuron that picked up the pain stimulation will synapse with a second interneuron in the spinal cord. • 3. The second interneuron will carry information to opposite side of the spinal cord, where the interneuron will synapse with a motor neuron.

32. Anatomy of a Crossed-Extensor Reflex • 4. The motor axon carries the message out of the spinal cord through the anterior root. • 5. The motor axon will synapse with the muscles of the thigh which results in: knee extension.

33. Importance of Testing Reflexes • Many of our somatic reflexes can be assessed. • Testing somatic reflexes is an important diagnostic tool. • Assessment of somatic reflexes tells us something about the condition of the nervous system (usually the CNS). • If a reflex is distorted, exaggerated, weak or absent this may indicate a problem in the nervous system. • This is usually one of the first signs of nervous system pathology.

34. Importance of Testing Reflexes • Pathology associated with abnormal reflexes • Absent reflexes • Demyelination • Muscular dystrophies • Spinal cord injuries • Closed head injuries • Exaggerated reflexes • Spinal stenosis – compression of spinal cord.

35. References • Armbruster, R., Challgren, B., & Jensen, M. WebAnatomy. Retrieved January 16, 2003, from University of Minnesota Web site: http://www.gen.umn.edu/faculty_staff/jensen/1135/ • Anatomy and Physiology: Spinal Cord, Nerves and Muscles. Retrieved December 11, 2002, from KidsMove Web site: http://www.remove.org/kidsmove/ana.html • Kingman, J. Brain Galaxy Art Gallery. Retrieved January 16, 2003, from Web site: http://www.bowdoin.edu • Nosek, T., & Stoney, S. (1999). Essentials of Human Physiology. Gold Standard Multimedia. • Reflexes. Retrieved December 11, 2002, from Newton’s Apple Web site: http://www.ktca.org/newtons/13/rlxes.html • Rutherford, K. What are reflexes? Retrieved December 11, 2002, from KidsHealth Web site: http://kidshealth.org/kid/talk/qa/reflexes.html

36. References continued • Scarbrough, M. & Wolf, M. The JayDoc HistoWeb. Retrieved January 16, 2003, from University of Kansas Web site: http://www.Kumc.edu/instruction/medicine/anatomy/histoweb • Seeley, R., Stephens, T., & Tate, Phillip. (2003). Anatomy and Physiology. New York: McGraw Hill.

37. Testing Your Reflexes • Work with a partner • 1. Test the speed of your reflexes. • Involuntary reflexes can occur as fast as 320 miles per hour. • Conscious muscular responses occur much slower – this is what we will test first. • 2. Testing somatic reflexes • Testing involuntary somatic reflexes. • We will not be using these reflexes as diagnostic tools.